A currently foreseen development of communication in cellular networks involves numerous small autonomous devices, which transmit and receive only small amounts of data (or are polled for data) occasionally, e.g. once a week or once per minute. These devices are sometimes referred to as Machine Type Communication (MTC) devices, Machine-to-Machine (M2M) devices or just Machine Devices (MDs), and are assumed not to be associated with humans, but are rather sensors or actuators of different kinds, which communicate with application servers within or outside the cellular network. The application server configures and receives data from the MTC devices. Hence, this type of communication is often referred to as machine-to-machine (M2M) communication.
So far focus has been directed to MDs being directly connected to the cellular network via the radio interface of the cellular network. However, a scenario which is likely to be more prevalent is that MDs connect to the cellular network via a gateway. In such scenarios the gateway acts like a communication device (which may also be denoted user equipment, UE) towards the cellular network while maintaining a local network, typically based on a short range radio technology towards the MDs. Such a local network, which in a sense extends the reach of the cellular network (to other radio technologies but not necessarily in terms of radio coverage), has been coined capillary network and the gateway connecting the capillary network to the cellular network is referred to as a capillary network gateway (CGW).
FIG. 1 illustrates such capillary network 1, comprising a number of machine devices 21, 22, 23 communicating with a CGW 41, 42 over a first air interface 3 typically implementing a short range radio technology. The CGWs 41, 42 are in turn communicating with a node 51, 52 of the cellular network 6 over a second air interface 7. An application server 8 is also illustrated. The MDs 21, 22, 23 are typically relayed to such an application server 8 through the cellular network 6, whereby the MDs 21, 22, 23 are able to exchange data with applications of the application server 8.
When designing the capillary network several considerations have to be made. All MDs need of course to be able to reach a CGW and the selection is today based on some channel quality metric. The number of CGWs thus needs to be high enough to ensure that all MDs are sufficiently close to a CGW to have a channel quality enabling communication with the application servers. This is in contrast with the desire of the operators of the capillary networks, who would like to keep down the costs of the networks, e.g. by providing as few CGWs as possible. An increased transmission power could be used, enabling MDs to reach CGWs that are located further away and thereby reducing the number of required CGWs. However, the MDs are most often battery operated and an increased transmission power is therefore disadvantageous e.g. in that the energy consumption would increase. The MDs have to be very energy efficient, as external power supplies are typically not available and since it is neither practically or economically feasible to frequently replace or recharge their batteries.
There is thus a tradeoff between the requirement of high communication reliability and the costs related thereto.
Further, the capillary network may comprise both advanced CGWs that are connected to an electricity mains supply as well as more simple CGWs that are battery operated like the MDs. Irrespectively of type of CGWs, they should be managed efficiently in order to provide reliable communication means for the MDs while keeping down the operating costs of the capillary network.